U.S. Pat. No. 5,279,999 describes the synthesis of various bis-aryl cyclopentadienyl Group IVA metal dihalides. The adduct of an aryl lithium and cyclopenteneone is treated with an acid to obtain the arylcyclopentadiene which is deprotonated and reacted with a Group IVA metal tetrahalide.
A preparation of pentamethylene fulvene: ##STR1## from cyclopentadiene and cyclohexanone in methanol in the presence of pyrrolidine and conversion of the deprotonated fulvene to [(1-cyclohexen-1-yl)Cp].sub.2 ZrCl.sub.2 is disclosed in Erker, et al., Chem. Ber. (1991) 124:1301-1310.